Method of forming spiral thread lock



Jan. 5, 1965 ROSAN ETAL 3,163,872

METHOD OF FORMING SPIRAL THREAD LOCK Original Filed July 25, 1960 3Sheets-Sheet 1 I a6 48a.

INVENTOR.

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arrow/5V Jan. 5, 1965 J. RosAN ETAL 3,163,872

Onginal Filed July 25, 1960 &

INVEN TOR .Zs K7607! a. db arm/1M5? Jan. 5, 1965 J. RosAN ETAL METHOD OFFORMING SPIRAL THREAD LOCK 3 Sheets-Sheet 3 Original Filed July 25. 1960INVENTOR. I I o se Krsarz BY J7Z ertJZi/ [z 75m? MUG/EVE? amma UnitedStates l atent O 3,163,872 WTH'SD F FORMING SPIRAL THREAD LGCK JoseRosin, San Juan Gapistrano, and Albert Jack La Torre, Santa Ana, Califassignors to Rosz'm Engineering Corporation, Newport Beach, Calif., acorporation of California Qriginal application Juiy 25, 1960, Ser. No.45,855, now Patent No. 3,081,808, dated Mar. 19, 1963. Divided and thisapplication Aug. 28, 1961, Ser. No. 134,282 9 Claims. (Cl. -86) This isa division of application Serial No. 45,055, filed July 25, 1960, whichissued into Patent No. 3,081,808 on March 19, 1963.

The present invention relates to a method of making a threaded insertwith a spiral thread lock. This invention finds particular usefulness inmaking the inserts described in the aforesaid Patent No. 3 ,081,808.

The present inserts ditfer from all prior inserts in that they have aside wall of less radial thickness than that found in any prior inserts.The present inserts are further characterized by having higher strengthcharacteristics, greater hardness and greater ductility than is found inany prior inserts. It has been found that very thin walled inserts madein accordance with the teachings disclosed hereinafter, will develop aholding power markedly superior to that of previously known, relativelythick walled inserts of the same internal size.

Inserts made in accordance withthe principles of the present inventionand having internal and external threads are designed so that theexternal threads are one size larger than the internal threads; theexternal threads preferably being made less than full standard depth inorder to provide an uninterrupted thin-walled, radially flexible columnbetween the internal and external threads.

One of the principal features of the present inserts is that the insertsmade by this method not only embody means for permanently locking theinserts against rotation in the threaded bodies or members in which theyare mounted, but also may embody internal locking threads for preventinga bolt, stud, or other. fastener mounted therein from becoming looseunder conditions of excessive vibration. In this connection, theinternal lock is formed by slightly depressing the root of one or moreconvolutions of the external thread in a spiral pattern conforming tosaid one or more convolutions to correspondingly modify the internalthread by reducing its diameter to form locking threads providing aninterference fit with any fastener mounted therein.

Another advantage of the present invention is that the internal lockingthreads can be formed at any desirable point along the length of theinserts, or the inserts may be provided with locking threads at aplurality of points along their length.

Accordingly, the principal object of the invention is to provide amethod of making a one-piece lockable insert, and a method of providingan internal locking thread in an insert.

Another object is to provide a method of making an insert havinginternal locking threads and flexible side walls providing unusuallyhigh wear resisting characteristics enabling a fastener to be mounted inand removed from the insert a great number of times without damage tothe internal locking threads, and without reducing the effectiveness ofthe locking action of the internal locking threads.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a greatly enlarged quarter sectional view of an insertembodying the principles of the present invention;

FIG. 2 is a plan view of the insert of FIG. 1;

3,163,872 Patented Jan. 5, 1965 FIG. 3 is a fragmentaryverticalsectional view through a body having a threaded bore that iscounterbored at its outer end and adapted to receive the insert of FIG.1;

FIG. 4 is an elevational view, partly in section, of. an

insert having an internal thread lock and a modified driving groovearrangement;

FIG. 5 is a quarter sectional view of an insert of the type shown inFIG. 1, but modified to include axially spaced internal locking threads;

FIG. 6 is an elevational view of a standard stud threaded at both ends;I

FIG. 7 is a view showing the stud of FIG. 6 mounted in the insert ofFIG. 5, the insert being shown in crosssection;

FIG. 8 is a diagrammatic vertical sectional view of an insert of thetype shown in FIG. 4 disposed between the plate dies used for rollingthe locking thread in the insert; a

FIG. 9 is a greatly enlarged diagrammatic view illustrating a portion ofthe insert of FIG. 8 and a portion of the die that rolls the root of anexternal thread to form the internal locking thread, the latter beingindicated in dotted lines;

FIG. 10 is a diagrammatic sectional view illustrating a step in anothermethod of rolling the external thread prior to forming a locking threadwithin the insert;

FIG. 11 is a diagrammatic sectional view illustrating the step ofrerolling the external thread to form the internal locking thread;

FIG. 12 is a greatly enlarged diagrammatic view of a portion of theinsert and die that rolls the internal locking thread. 7

Referring to FIGS. 1 and 2, the new insert is generally identified bythe numeral 10 and comprises a tubular body 12 provided with externalthreads 14 and internal threads 16. The external threads 14 have a majoror crest diameter indicated by the dimension A, and a minor or rootdiameter indicated by the dimension B. The external threads 14 areshallower in depth than a standard thread of the corresponding size andpitch, so that the diameter B of the thread root 15 is larger than theroot diameter of a standard size thread, as will be explained more fullyhereinafter. The internal threads 16 have a major or root diameterindicated by the dimension C and a minor or crest diameter indicated bythe dimension D. The diameters C and D correspond to those of a standardsize thread. In other words, the internal threads 16 are preferablyunmodified in order that they can receive any fastener provided withcorresponding standard threads.

The insert 10 has a radial wall thickness E equal to /2(B-C) that issubstantially less than has been provided heretofore in inserts of thesame general type. Such thin wall construction has been made possible byforming the insert 10 with external threads 14 one size larger than theinternal threads 16, and preferably modifying the external threads 14 bymaking their depth substantially less than standard depth.

According to the present invention, the external threads 14 have aradial depth less than the standard depth. The use of a modifiedexternal thread makes it possible to maintain a continuous thin wall orcolumn 18 of minimum thickness E throughout the internally threadedlength of the insert. The insert 10 has a counterbore 20 at its upperend 22 of a depth equal to about twice the pitch of the external threads14, but this depth may be varied as desired. The counterbore 20 isformed by a cylindrical wall 24 and a beveled Wall 26 extending on anangle of 45. The wall 24 has a. diameter F that is preferably a feWthousandths of an inch larger than the root diameter C of the internalthreads 16, so that a thin expandable wall 28 having a radial thicknessof a dimension G is provided at the outer end of the insert.

Thus, the expandable wall 28 is slightly thinner than the column wall18.

The internal threads 16 are intersected by six longitudinal V-shapedgrooves 30 defining a hexagon shaped recess within the insert andadapting the threads 16 to be engaged by a hexagonal drive member ofcorresponding shape and'size for driving the insert into a threadedbore. The sides 32 of the grooves 39 intersect an angle of 120-", andthe distance across the flats of the hexagon has the dimension LFIG. .2.The diametrical distahce between the apices of the grooves 39 isrepresented by the dimension J. The grooves 30 need not extend for thefull length of the inser-t 10 and may be terminated at any desireddepth; The external threads 14 in the region of the counterbore 20 areknurled or longitudinally serrated through at least two convolutions toprovide relatively sharpte'eth 34 for engaging a surrounding body toform a permanent lock therewith. The teeth 34 have sides of volu'teshape due to the formation thereof by serrated rollers (not shown). Thelower end of the insert 10 is chamfered internally and externally on anangle of about 30, as indicated at 36 in FIG. 1. The knurling operationraises the crest of the threads 14 in forming the teeth 34, so that thediameter K across the points of the teeth is a few thousandths of aninch greater than the original crest diameter A.

As has been indicated. above, it is preferable to make the externalthreads 14 shallow, or of less than standard depth. In accordance withthe present invention, it is also preferred to make the threads 38, FIG.3, in the insert-receiving bore 40 in a parent body 42 less thanstandard height, in view of the following:

If theshallow-depth external threads "14 are used with an unmodifiedbore thread, excessive torque would be required to mount the insert 10in the bore, due to the interference between theorests of the borethreads and the root of the external threads 14. In addition toexcessive torque, there would be the possibility of distorting orcrushing the thin-walled inscrt'while it is being mounted in the bore.In the, case of mounting the insert in Plexiglas, Lucite and otherplastic materials, the excessive stress concentration would causecrazing in the plastic. In order to avoid the foregoing 'difiicnlties,the bore 40 to receive the insert 10 is drilled with a tap drill of adimension larger than would normally be used in providing a bore to betapped for a standard thread corresponding to the size of the externalthreads 14 on the insert. Accordingly, and as is shown in FIG. 3,

the body of parent material 42 is drilled to provide the bore 40 havinga dimension L. The outer endof the bore 40 is provided with acounterbore 44 having a cylindrical Wall 46 of a diameter M and abeveled wall 48 extending on an angle of about 30. The diameter M issuch as to receive the locking teeth 34 with a mini? mum of radialclearance. Hence, the diameters K and M are made almost equal.

It is not essential that the bore .40 be 'counterbored since the presentinsert can be used with a bore that is threaded throughout its length.In such case, the points of the teeth 34 may engage the root of thethreads, but this would not be objectionable since the teeth would reamout the root to make their own way, if necessary. In either instance,the diameter L of the drilled bore 40 is made greater than the crestdiameter of the corresponding standard thread size, so when threads, 38are tapped in the bore 40, the crests are truncated. as indicated at 48ain FIG. 3, respectively.

The diameter of the bore threads 38 is such that the crests 48a do notengage the root 15 of the external threads 14 of the insert 10. Theclearance thus provided eliminates stress concentration in these areas.Thus, it is simpler and more practical, in the interest of providing thethin wall 18 in the insert 10, to adapt the bore 40 in the body 42. toreceive a modified external thread 14 (by using an oversize tap drillfor the bore 40) rather 4 than modifying the internal threads 16 of theinsert 10 so that only special fasteners could be used therewith.

It will be understood, of course, that the advantages of the insert 10can be realized by following the less desirable practice of making theinternal threads 16 shallow and using a standard external thread 14.

In making the insert 10, a solid rod or bar of stock (not shown) ofsuitable met-a1 is center-drilled at one end, and a portion of the endis rough turned and then finished to the desired outside diameter A, ascan be readily visual: ized. The external threads 14 are then rolledinto a predetermined length of the rod. From one of three convolutionsof the threads 14 at the threaded extremity of the rod are next knurledto form the teeth 34, The rod is then rough drilled to provide a bore16a and the finished counterbore 2-0. The bore 16a is then finish.-reamed to the minor diameter D of the internal threads 16. The rod isthen cut oil by a parting tool at the end of the threaded portion remotefrom the teeth 34. The work piece is then finish-faced, and internallyand externally chamfered as, shown at 36,.at the end remote from thecounterbore 20.

The cut off work piece in the foregoing state is then rough-tapped toremove a major portion of the metal that will form the internal threads16, and is then broached to provide the driving grooves or flutes 30.The internal thread 16 is then finish-tapped, completing machining ofthe insert 10 of FIG. 1, which is then heat-treated to give it ahardness of 40 to46 on the Rockwell C scale.

It will be noted from the foregoing that the teeth 34 are formedbefore'the bore 16a is drilled and the counterbore 20 is formed. Thisprocedure assures good knurling without distorting or damaging theinsert material.

FIG. 4 illustrates a modified form of insert 49. The insert 49 alsodiffers from the inserts previously described herein in that it isprovided with a unique internal IQCk'. ing thread 50 located at a pointabout midway of the height of the insert and extending through about 1/2 convolutions of the internal 51 The internal look: ing thread 50provides a loci; for any threaded fastener that is mounted thereon. Themanner which the loch-1 ing thread 50 is formed will be described indetail later.

FIG. 5 shows an insert 52, similar to the insert 10, but :wherein theroot of the external thread 14 has been depressed at longitudinallyspaced points to provide two internal. locking threads 50. The lockingthreads 50 are preferably located beyond the second convolution Of theinternal lead thread 16 in order to enable a fastener to have asubstantial start in the insert enga ing before the locking thread 50.Any number of locking threads 50 may be provided in the insert,depending upon the length. of the insert. It will be obvious, of course,the more locking threads that are provided, the greater will be thetorque resistance oflfered by the insert to backing out of a fastener.The use of two locking threads, as shown, doubles the locking elfect ofthe single thread shown in FIG. 4.

The insert 52 is especially adapted to be used with a standard stud '53of the type shown in FIG. 6, which has threads 54 and '55 at itsopposite ends. FIG. 7 shows the insertSZ mounted upon the threads 54 atthe lower. end of the stud 53. The internal locking threads '50effectively lock the stud 53 against turning, so that when the insert 52is locked in a parent body, the stud 53 may be removed without backingthe insert out of the pawn bQdY- More? over, any fastener, such as anut, mounted upon the threads .55 can be removed without backing thestud 5 3 out of the insert 52.

The locking threads 54} are preferably formed in the insert 49, FIG. 4,after it has been otherwise completely machined and heatstreated toharden the same. This has the advantage that the dimensions of thelocking thread 50 can be held to close tolerances since no sizedeviation is introduced by subsequent heattreatnient. The lock: ingthreads 50 are formed by a cold-rolling operation.

FIG. 8 diagrammatically illustrates the manner in which the lockingthread 50 is formed. Thus, an insert such as the insert of FIG. 1, isplaced between a pair of die-rolling plates 56 and 57. The plate 56 issimilar to the plate originally used to roll the shallow external thread14, except that the thread forming ridges 58 are ground off so that theydo not engage the root of the external thread 14, but clear the same bya few thonsandths of an inch. No change is made in thesides of theridges 58. Hence, they engage and support the flanks of the thread 14against distortion during the rolling of the locking thread 50.

The die-plate 57 is positioned on the opposite side of the insert 10 andis provided with a single ridge 59 located at the point where thelocking thread 50 is to be formed in the insert. The ridge 59 is ofslightly greater height than the ridges on the die-plates previouslyused to form the threads 14 and may have the configuration of a die forforming a thread of standard depth. The sides of the ridge 59 arepreferably parallel with the flanks of the threads 14 but may berelieved slightly to permit drawing in of the metal during rolling. Thedifference in angle may be about one degree at each side, so that theangle of the sides of the ridge 5? is about 58, compared with the 60angle of the threads 14. The foregoing relation is diagrammaticallyshown in FIG. 9 wherein a portion of the insert 10 and a portion of thedie-plate 57 are shown to greatly magnified scale. It will be noted thatthe face of the ridge 59 is narrower than the root 15 of the thread 14so that a distinct, depressed, spiral pattern groove 6% having thecontour shown in dotted lines is formed in the rotor.

During the rolling of the locking thread 58, the dieplate 56 supportsthe flanks of the thread 14 to prevent distortion thereof, while thedie-plate 57 applies pressure to the insert 10 to depress the root 15inwardly about .001", or more, depending on the diameter of the insert,to the depth indicated by the dotted line 64 As the dieplate 57 ispressed toward the insert 10 and moved relative thereto, the ridge 59 indepressing the root 15, as indicated above, will cause a correspondingportion of the internal thread 16 to be deformed inwardly to reduce itscrest diameter and form a locking thread 59, the typical distortion andcontour of the internal threads 16 being indicated by the dotted line61. In view of the fact that the external threads 14 and the internalthreads 16 have a diiferent pitch, the rolling of the root 15 of theexternal thread effects a slight change in the lead of the lockingthread 50, as illustrated, which enhances the locking action of thethread.

During the rolling of the locking thread 51), the insert 10 ispreferably rotated through about 1 /2 turns, so that locking thread 50extends through about 1 /2 convolutions of the internal threads 16. Thelocking thread 50 may extend through two convolutions, but preferablynot less than one. Extending the locking thread 56) through an angle inexcess of 360 will avoid unequal pressure on the locking thread andinsure a uniform resistance to rotation of a fastener throughout theperiphery of the fastener. Consequently, a uniform torque is required toturn the fastener relative to the locking thread 50.

One of the unique features of the locking thread 5t combined with theresilient, ductile side wall construction of the present insert is thatthe insert is capable of breathing or yielding and expanding when thelocking thread is engaged by a fastener. Torque tests have shown thatthe present insert has the unexpected and unusual characteristic ofrequiring breakaway torque equal to the drive torque applied to thefastener, and in some instances the breakaway torque has exceeded thedrive torque. In prior fasteners, the breakaway torque is ir1- variablyonly a minor fraction of the drive torque. Hence, the present insert isfar superior to all prior inserts in resisting loosening underconditions of severe vibration.

FIGS. 10, 11 and 12 diagrammatically illustrate another method offorming a locking thread 50 in the insert 10. FIG. 10 illustrates oneend of a piece of bar stock X having a center drill Y formed in one endthereof and engaged by a lathe center Z, the latter being shown indotted lines. The external thread 14 is formed in the bar stock by oneor more rollers or dies 62. The die 62 shown has ridges 63 that roll themajor portion of the length of the external thread 14 to the desiredshallow depth. A single ridge 64 on the die 62 is of less height thanthe remaining ridges 63, so that about 1 /2 convolutions, indicated at65, are shallower than the remaining root portions 15 of the externalthread 14.

The additional machining operations on the insert 10, described inconnection with FIG. 8, are then performed upon the bar stock X, so thatthe resulting insert 16X has the structure illustrated in FIG. 11. Theinsert 10X is heat-treated to harden the same in the same manner as theinsert 10. After heat-treating, the external threads 14 are rerolled bya cold-rolling operation to form the internal locking thread St). Thererolling is preferably effected by die plates 56'. and 57 which, as inFIG. 8, do not engage the teeth 34 of the serrated threads. These dieplates have ridges 58' all. of which are of the same height, so thatduring the rerolling operation, the shallow root portion 65, see FIG.12, is depressed inwardly from the position indicated in dotted lines tothe full line position marked 65', which corresponds to the depth orroot diameter of all of the remaining external threads 14. During thererolling operation, both die plates 56 and 57 cooperate to effectdisplacement of the root portion 65, and simultaneously support theflanks of the remaining external threads 14 against distortion. As thedie plates 56 and 57' apply pressure to press the root portion 65inwardly, the ridges 58' cause a corresponding portion of the internalthread 16 to be deformed inwardly to reduce its crest diameter and formthe locking thread 50, the distortion of the internal threads it beingindicated by the dotted lines 61. The rolling of the root portion 65 ofthe external thread 14 effects a slight change in the lead of thelocking thread 50, as shown, which enhances the locking action,

The method of forming the locking thread 50 illustrated in FIGS. 10, 11and 12 has the advantage over the method illustrated in FIGS. 8 and 9,of providing an external thread 14 wherein the root diameter is uniformthroughout the length of the insert.

It will be understood that any one of the internally threaded insertsdisclosed herein can have one or more locking threads formed in theinterior thereof. It will also be understood that while certain insertshave been shown mounted in a bore of a certain type, any given insertcan be mounted and used in any other type of bore shown herein.

It will also be understood that the principle of making the externalthread larger than the internal thread by one thread size is applicableto both fine threads and coarse threads. However, by way of illustrationand not limitation, the following example is given relative to afinethread insert having a 4 inch internal thread with 28 threads perinch, and a inch external thread with 24 threads per inch. Such aninsert will have the following principal dimensions, which should beconsidered in connection with FIG. 1, and'with the understanding thatthey will vary within acceptable tolerances:

It will be noted from a comparison of the minor diameter B of theexternal thread 14 with the major diameter C of the internal thread 16that the side wall 18 of the insert is about 0.0117" thick. In thesmallest and thin nest inserts made in accordance with this invention,it is preferred to maintain a minimum side wall thickness of not lessthan 0.008" with a preferred minimum thickness of 0.011. It is to beunderstood, however, that this side wall thickness will vary with thesizes of internal and external threads employed in the inserts. Hence,the minimum thickness may exceed 0.020" in some inserts, but in anyevent, the side wall thickness in each insert will be substantiallythinner than in prior inserts of the same internal thread diameter.

Other typical thread combination sizes of internal and external threadsthat may be used for the present insert are. as follows:

Inches 0.25

Minimum Standard Mini- Internal External Modified Root mum Thread ThreadRoot Dia. Int. Wall Size Size Dia. Thd. Thick- Ext. (Inches) ness Thd.(Inches) (Inches) -32 4-28 0.2120 0. 1900 0. 0110 54-28 ")1 e-24 0.2735' 0. 2500 0. 0117 it e--24 %24 0. 3355 0. 3125 0. 0115 24 Z4 a-20 0.3960 0. 3750 0. 0105 '}i (r20 r20 0. 4580 0. 4375 0., 0102 l-ZO Mo-2 40. 5240 0. 5000 0. 0120.

In the above table, column 1 indicates the size of the internal threadof the insert; column 2 the size of the external thread; column 3 theminimum root diameter of the external thread in inches, which is lessthan standard; column 4 the standard root diameter of the internalthread in inches; and column 5 the minimum wall thickness of the insertin inches. It will be noted that the minimum wall thickness shown is0.0102" and that for the sizes shown, the wall thickness varies from0.0102" to 0.0120"; It will be clearly understood that these wallthicknesses will varydepending upon the variations in allowabletolerances for the given threads, between'ma-ximum and minimum. In anyevent, the wall thickness of any given insert made in accordance withthe principles of this invention will be less than that of prior insertsof the same internal thread size.

The inserts disclosed herein may he made of any suitable material. Ithas: been determined that a stainless steel known in the metallurgicalfield as Armco'174P H is an ideal material for use in making the presentinserts. Another stainless steel known inthe industry as Armco 1710PHmay be used where a non-magnetic material is desired for the insert.Certain aluminum alloys can also he used, including the well knownaluminum alloy identified as 2014T6. The, latter may be used where ahard, light-Weight insert is desired. In this, connection, the presentthin-walled inserts made of stainless steel are characterized by theirsurprising lightness. For example, 1000 stainless steel inserts having a/4-28 internalthread and a 71 -24 external thread, weigh only 2.7 lbs.The use of stainless steel and aluminum alloys is further preterablebecause of their corrosion resistant properties.

A steel alloy, A.I.S.I. #4130, has also been tound satisfactory.Although it does not have corrosion resistant 8 properties, it does havethe strength characteristics of the above stainless steels.

The stainless steel materials mentioned above are particularly wellsuited for use in making the present thinwalled inserts for the reason,that they can be heat-treated to give the inserts the desired highhardness, high ductility and high modulus of elasticity required withoutrendering the same brittle or introducing other undesirable characteristics.

One of the preferred stainless steel materials for making the presentinserts Armco 17-4PH has the following physical properties at roomtemperature:

Ultimate tensile strength 190,000 lbs, p.s.i.

(pounds per square. inch). Yield .02% 170,000 p.s.i. Double Shear130,000 p.s.i. Elongation in two inches 10%.

Reduction of cross sectional area in test piece 37.5 to Rockwellhardness (C Scale) 40 to 46.

A single internal locking thread of 1 /2 convolutions provides torqueand pull-out resistance that far exceeds the requirements of MilitarySpecifications N-25027 (ASG),

Actual tests have also shown that the internal lock thread is capable ofmaintaining torque resistance meeting specifications even after 600cycles of insertion and removal of bolts from the insert. This extremelylong life of the locking thread 50 is believed to be attributable to thehardness of the material of the insert and tothe fact the side wall 18of the insert is thin and resilient, enabling said side wall to flexoutwardly when the locking thread is engaged by a fastener, rather thanremaining rigid and causing excessive wear on the fastener threads andlocking thread.

Any of the inserts disclosed herein can have more than one lockingthread formed therein, if desired.

While several methods of making a one-piece lockable insert having aninternal locking thread have been disclosed herein, it will beunderstood that minor variations may be made therein without departingfrom the principles of the invention or the scope of the annexed claims.

We claim:

1. The method of making a threaded insert with, an internal lock,comprising the steps of: forming external and internal threads in ametal body with the external thread one size larger than the internalthread and with a Wall thickness between the root diameters of saidinternal and external threads of not less than .008"; heat treating thebody to harden the same; and cold-rolling in a spiral pattern through atleast one convolution, the root portion only of said external threadwhich is disposed opposite a crest of an internal thread so as todepress the same to a depth below the original root diameter of saidthread, whereby to displace corresponding portions of the internalthread to reduce the crest diameter thereof to provide an internallocking thread.

2. The method of making an insert as defined in claim 1, includingforming the external thread to a. depth sub.- stantially less than thedepth of a standard thread of the same diameter and pitch.

3. The method of making a threaded insert, with an internal lock,comprising the steps of: forming an external thread on a metal body of adepth substantially less than that of a standard thread of the samemajor diameter and pitch; forming a standardthread interiorly of saidbody of a size to provide a thin: wall portion between said external andinternal threads; heat treating the body to harden the same; andcold-rolling in a spiral pattern through atleast one convolution, theroot portion only of said external thread which'is disposed opposite acrest of an internal thread so as to depress the same to a depth belowthe original root diameter of said thread, whereby to displacecorresponding portions of the internal thread to reduce the. crestdiameter thereof to. provide an internal peripheral locking thread.

4. The method of making a hollow insert, comprising the steps of:forming standard threads on the interior of the body of the insert;forming threads on the exterior of said body to a depth substantiallyless than the depth of a standard thread of the same diameter and pitch;and depressing the root of the external thread which is disposedopposite a crest of an internal thread through at least one convolutionof the external thread.

5. The method of making a threaded insert, with an internal lock,comprising the steps of: forming an external thread on a metal body:forming a thread interiorly of said body; heat treating the body toharden the same: and cold-rolling in a spiral pattern through at leastone convolution of the root portion of said external thread which isdisposed opposite a crest of an internal thread so as to depress saidroot, thereby displacing a corresponding portion of the internal threadto reduce the crest diameter thereof to provide an internal, lockingthread.

6. The method of making a threaded insert with an internal lock,comprising the steps of: forming an external thread on a metal body of adepth substantially less than that of a standard thread of the samemajor diameter and pitch with 1 to 2 convolutions of shallower depththan the remaining threads; forming a standard thread interiorly of saidbody of a size to provide a thin wall portion between said external andinternal threads; heat treating the body to harden the same: andcold-rolling in a spiral pattern the root portion only of said 1 to 2convolutions of said external thread which is disposed opposite a crestof an internal thread so as to depress said root to a depth equal tothat of said remaining external threads whereby to displacecorresponding portions of the internal thread to reduce the crestdiameter thereof to provide an internal locking thread.

7. The method of making an insert as defined in claim 1, including thestep of supporting the flanks of the external thread against distortionduring the cold-rolling of the root portion of said external thread.

8. The method of making an insert, as defined in claim 1, in which theexternal and internal threads are formed on a stainless steel body andsaid body is heat treated to a hardness of to 46 on the Rockwell Cscale.

9. The method of making an insert, as defined in claim 1, wherein therolling of the root portion of the external thread is confined toapproximately one and one-half convolutions of said root portion throughabout one and onehalf convolutions.

References Cited in the file of this patent UNITED STATES PATENTS1,692,497 Furlan Nov. 20, 1928 2,444,145 Rosan June 29, 1948 2,791,787Neuschotz May 14, 1957 2,795,221 Braendel June 11, 1957 3,065,983Flumerfelt Nov. 27, 1962 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION PatentNm 3,163,872

January 5, 1965 Jose Rosain et al Itis hereby certified that errorappears in th ent requiring corr e above numbered patection and that thesaid Letters P corrected below.

atent should read as Column 3, line 67, strike out respectively"; column5, line 32, for "rotor" read -root column 10, lines 18 and 19,

rough about one and one-half convolutions".

Signed and sealed this 5th day of- October 1965.

SEAL) Attest:

ERNEST W. SWIDER \ttesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. THE METHOD OF MAKING A THREADED INSERT WITH AN INTERNAL LOCK,COMPRISING THE STEPS OF: FORMING EXTERNAL AND INTERNAL THREADS IN AMETAL BODY WITH THE EXTERNAL THREAD ONE SIZE LARGER THAN THE INTERNALTHREAD AND WITH A WALL THICKNESS BETWEEN THE ROOT DIAMETERS OF SAIDINTERNAL AND EXTERNAL THREADS OF NOT LESS THAN .008"; HEAT TREATING THEBODY TO HARDEN THE SAME; AND COLD-ROLLING IN A SPIRAL PATTERN THROUGH ATLEAST ONE CONVOLUTION, THE ROOT PORTION ONLY OF SAID EXTERNAL THREADWHICH IS DISPOSED OPPOSITE A CREST OF AN INTERNAL THREAD SO AS TODEPRESS THE SAME TO A DEPTH BELOW THE ORIGINAL ROOT DIAMETER OF SAIDTHREAD, WHEREBY TO DISPLACE CORRESPONDING PORTIONS OF THE INTERNALTHREAD TO REDUCE THE CREST DIAMETER THEREOF TO PROVIDE AN INTERNALLOCKING THREAD.